Beebe Bathysphere, 1934

© akg-images / US NAVY/SCIENCE PHOTO LIBRARY

From peephole to panoramic view of the deep sea

For humans, the only way to view the deepest corners of the sea is through the window of a submersible, and the larger the window, the more can be seen. PLEXIGLAS® turns the ocean into a panorama with an all-round view.

The question is, however, why humans want to dive deeper than their lung capacity allows? What fascinates humans about an environment that is hostile to them? The answer is simple: curiosity. Curiosity is one of the strongest motivators for humans. This is because the area of the brain which is stimulated by the acquisition of new knowledge is closely linked to the release of dopamine, a hormone often described as pleasure hormone. This link is one of the main driving forces behind the evolution of mankind – and the development of the submersible.

Alexander the Great – the first marine explorer

According to historical reports, Alexander the Great (356-323 BC) explored the sea floor with the help of a diving bell made of glass, while Leonardo da Vinci created a submersible and a diving suit in 1515 – at least on paper. The first seaworthy submersible was built by David Bushnell in 1776. It was given the name “Turtle” and was manually operated by the pilot. The development of submersibles from the mid-19th century onwards was mainly driven by military objectives. Humans first used a submersible for research purposes in 1930, diving into the deep sea in the bathysphere, a steel ball with portholes.

Three portholes for the deep sea

A bathysphere is a spherical steel pressure chamber which is lowered into the sea from a ship using cable riggings. The first bathysphere was built in 1930 by American professor William Beebe and engineer Otis Barton. The viewing windows were made from quartz glass.

Chasing world records with PLEXIGLAS®

The first submersible with two small portholes made from PLEXIGLAS®, the brand acrylic glass from Evonik (at the time still Röhm & Haas), was designed in a similar manner. The “Trieste” was launched in 1960 with the ambitious target of exploring the floor of the Mariana Trench, the deepest part of the world’s oceans. Swiss scientist Jacques Piccard designed and built the unique submersible with which he and American Marine officer, Don Walsh, descended almost 11,000 meters. Since then, this pioneering achievement has only been repeated by a single human, film director James Cameron, who descended to the deepest part of the world’s oceans in a far more modern submersible in 2012.

The windows of the ‘Trieste’ were manufactured from PLEXIGLAS®, as the plasticity of this material has always proven absolutely reliable.

Jacques Piccard
designer of the “Trieste” submersible

Keeping an eye on research

Although the “Trieste” provided the first look at the depths of the ocean, it was almost like looking through a keyhole as the technology at the time did not allow for larger windows. As the whole idea of deep sea diving is to explore the ocean, developers focused their efforts on building submersibles with ever larger windows.

This resulted in a private initiative of Austrian engineers creating the “Austria 1” in 1986/1987. This submersible was equipped with a viewing dome and a much larger bow window, both of which were manufactured from the brand acrylic glass. “PLEXIGLAS® was the ideal material for submersibles even back then, as it allowed the pilots a view of the deep sea without any optical distortions and did not fog up despite the temperature difference between the exterior and interior. At the same time, a PLEXIGLAS® window is also extremely safe as it can withstand the tons of water pressure, while also having additional safety reserves for the compression load,” explains Wolfgang Stuber, special glazing specialist for the PLEXIGLAS® brand.

Hunting for prehistoric fish

In 1989, the “JAGO” submersible was built for the Max Planck Institute for Behavioral Physiology. It was constructed to dive to depths of 400 meters to search for coelacanths, which are considered living fossils. This submersible provided the first comprehensive view of the underwater world at greater depths thanks to its viewing dome made from PLEXIGLAS® GS 222. The special brand acrylic glass was manufactured specifically for the demands and particularly the high pressure experienced under water. At depths of 400 meters, which this submersible was constructed for, the pressure can be up to 3,600 tons. PLEXIGLAS® GS 222 was inspected by Germanischer Lloyd, a classification society for marine vehicles, and certified for its high quality. “JAGO” was also successful in its quest to find the rare fish.

The submersible was also used to examine the unique ecosystem off the coast of Norway. Source: YouTube/The Future Ocean

Deep sea in HD thanks to PLEXIGLAS®

“We desperately wanted a submersible which was made in Germany. Evonik worked together with us on every single detail in developing the dome.”

Joachim Jakobsen
Rebikoff-Niggeler Foundation

Another milestone in the history of submersibles is the “LULA 1000”. It was commissioned by the Rebikoff-Niggeler Foundation in 2011 in order to track down deep-sea squids. “LULA 1000” accommodates three crew members and is equipped with a PLEXIGLAS® viewing dome with a diameter of 1.4 meters. “To create a curved window of this size, we first had to develop a block of PLEXIGLAS® which was thick enough to withstand the water pressure. This window required a thickness of 17 centimeters,” remembers Stuber. “After such a block has been molded, it is then heated to over 150 degrees Celsius and shaped into a hemisphere under great pressure.”

The result is an almost semicircular window that provides a 150-degree view of the sea and is almost invisible under water. PLEXIGLAS® made it possible for the first high-definition films to be shot in the deep sea, with the almost alien world being recorded through the portholes of the submersibles without any distortion.

Die „LULA 1000“ verfügt über zwei Sichtkuppeln aus PLEXIGLAS®.

Descending into the world of the giant squid

“LULA 1000” is 7.5 meters long and 2.65 meters tall. She is equipped with two viewing domes, with the larger dome below the bow and the smaller dome (61 cm diameter) acting as the entry port. The submersible is equipped with electric motors, which can propel the researchers for up to five hours during their search for the incredible squids before needing to be recharged.

© Dave Mothershaw/Evonik Industries AG

Smiles all round

The step from a hemisphere to a complete sphere is not large, provided the right adhesive needed to glue the two halves together is available. To avoid distorting the view, however, the adhesive also has to exhibit the same high light transmission values as the PLEXIGLAS® itself, while also being able to withstand the great water pressure. “An adhesive which only sticks strongly to the connecting surfaces is simply not sufficient for the requirements here,” explains Stuber. “We therefore had to develop a method to invisibly and inseparably connect the two hemispheres, similar to cold welding.”

Milestone in development

With this special adhesive, Evonik was able to develop a new milestone in the history of submersible windows, together with the American company Triton Submarines LLC and processing partner Heinz Fritz Kunststoffverarbeitung GmbH. For the first time, it was possible to create a passenger cell built from two PLEXIGLAS® hemispheres which were glued together to create a sphere. The sphere of the “Triton 3300/3” submersible is large enough for three people to sit in comfort. The crystal-clear all-round view enabled the award-winning British wildlife filmmaker and naturalist, Sir David Attenborough, to record the worrying state of the Great Barrier Reef in astonishing clarity. A submersible with a panoramic view is not only of great interest for scientists, however – the super-rich are increasingly regarding these vehicles as status symbols.

The exterior diameter of the passenger sphere is 2.1 meters, while the walls are 17 centimeters thick, enabling “Triton 3300/3” to dive up to depths of one kilometer.

The sphere that opens up a new world

Despite the cutting-edge technology used in the construction of “Triton 3300/3”, the development of submersible glazing is by no means at its limits. “Manufacturers are currently working on submersibles for cruise ships, in which up to seven people can sit in comfort,” says Stuber, providing an insight into future projects. After the challenges with regard to shaping and joining have been mastered, the next step is to continuously increase the size of the passenger cells made from PLEXIGLAS®. “My personal dream, however, is an underwater hotel. The first plans for such a construction have already been drawn up,” says Stuber, as he dreamily looks out of the window.

Read more on submersibles with viewing domes made from PLEXIGLAS®:

Passion for the deep sea Interview with Kirsten and Joachim Jakobsen
The LULA1000 on the lookout for the giant squid
LULA1000 discovers a missing German submarine
Triton Submarines: Luxury in the deep sea
Diving down to the Great Barrier Reef 
Anglerfish: Sensational video from the deep sea